A commenter at this post writes:

When it costs hundreds of millions of dollars to fly a single Shuttle mission, I fail to see the problem with spending another 10 to fix the wiring.

The first problem is a misunderstanding of Shuttle costs. The marginal cost of a flight is not “hundreds of millions of dollars.” It’s probably somewhere between a hundred and a hundred and fifty million. The average cost is much more, but that’s not a useful number, because it can vary so much with flight rate (for example, when the flight rate is zero, as it has been since February, 2003, the average cost per flight is infinite, regardless of how much we spend on the Shuttle program).

The second problem is that, while ten million dollars may not seem like much in the context of a program that costs billions annually, the fact remains that NASA has a finite budget, and ten million spent on one item is ten million less available to be spent on something else, that might be more important. According to the article that the original post linked to, the odds of an uncommanded thruster firing resulting in a catastrophe are somewhere between one in ten thousand and one in a million (it doesn’t say if that’s on a per-mission basis, or totaled over the next twenty-odd flights). Assuming that those are valid numbers, with any degree of confidence, then the standard way to determine how much we should spend to prevent that event from happening would be to use the expected value of that event (probability times cost). The problem with that, of course, is assessing the value of either the Shuttle fleet, or the ISS, given that current policy recognizes them both as dead ends, in terms of future space policy.

That, in fact, is why I think that the CAIB recommendations should have been revisited after the new policy was announced. If the CAIB had known that the Shuttle was going to be retired at the end of the decade, they may not have recommended some of the more costly (and impractical) fixes for what would then have been recognized as a rapidly depreciating asset.